CSS contextual selectors enable you to define style commands that can be utilized by many
tags. When defining an contextual selector a period is placed before any
selector name (Not to be confused with ID selectors that begin with #).
When the contextual selector is used within a tag via class = the name of the
selector variable only (no period preceding). The following example with
define three contextual selectors (red_text, blue_text, and bold_text) and using
either <p>, <div>, or <span> tags will deliver the text with
the respective defined style.